<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  body{
    margin: 0;
  }
  .wrap {
    display: flex;
    flex-direction: column;
    min-height: 100vh; /*关键*/
  }
  ul{
    flex: 1;
    padding: 0;
    margin-top: 0px;

  }
  li{
    height: 100px;
    width: 100%;
    background: yellowgreen;
  }
  li:nth-child(odd){
    background-color: bisque;
  }

  button{
    width: 90%;
    height: 60px;
    background: #1677ff;
    border: none;
    border-radius: 10px;
    margin: 0 auto 20px;
    color: #fff;
  }
</style>
<body>
  <div class="wrap">
    <ul>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
      <li>哈哈哈哈</li>
    </ul>
    <button>按钮</button>
  </div>
</body>
</html>
